A number of devices employing containers for recovering silver from spent fixing solutions in photographic paper and film processes are known in the industry. These devices generally entail passing the solution containing silver salts through a metal which is above silver in the electromotive force series. The resultant chemical replacement action causes silver to be deposited within the container as the metal is dissolved. When the metal is exhausted, the contents of the container are processed at a refinery to recover the silver therefrom.
It is important to be able to control the release of silver-containing solutions into the environment. In order to safeguard the environment, it is important to remove the silver salts from solutions prior to disposing of the remaining solution. Attempts have been made, in the prior art, to fashion silver recovery systems that remove a large quantity of the silver from the solution prior to the disposal of the solution. Unfortunately, however, there remains a relatively large silver component in the solution after the solution passes through the silver recovery systems.
U.S. Pat. No. 3,369,801 issued to Harlan G. Hartman on Feb. 20, 1968, discloses a vessel in which the solution flows downward through a core tube to the bottom of the vessel and upward through steel wool to an outlet in the top of the vessel. The chemical reaction referred to above results in the deposition of silver within the vessel as the steel wool dissolves.
Metal screen is used as tho filler material in U.S. Pat. No. 3,630,505, issued to Byron R. MacKay on Dec. 28, 1971. The screen wire is therein said to be an improvement because steel wool fibers are quite small in diameter and are easily dissolved. As a consequence, large openings providing less resistive paths are created, permitting the solution to bypass the filler material and exit the vessel with the silver remaining in solution. In this patent the solution fluid is directed through a flow path from the inside surface of the container, through the screen, and upward from the bottom of the core tubing.
U.S. Pat. No. 3,655,175, issued to Victor Zeleny et al. on April 11, 1972 discloses canister in which the solution flows from the bottom of the core tube upward through metal shavings and a bed of neutralizing material of alkaline earth metal carbonate. This patent also discloses horizontal spacers or baffles separating the layers of shavings to prevent short circuitry of the solution as it flows upward through the filler material.
U.S. Pat. No. 3,840,217, issued to Michael T. MacKay on Oct. 8, 1974, discloses a plastic container with influent and effluent liquid passages in the form of T-connectors in its lid. The lower end of the influent tube is a T-shaped baffle for dispersing the influent solution. A U-shaped tube is connected between the influent and effluent connectors to accommodate solution overflow. Furthermore, the U-shaped tube is removable from the effluent connector to permit testing of the effluent solution to determine whether silver is being efficiently removed from the solution.
U.S. Pat. No. 4,441,697, issued to Donny L. Peterson et al., on April 10, 1984, discloses a plastic container with influent and effluent liquid passages. The lid has a hole for viewing the inside of the container. This device includes an elongated core with an aperture in its side extending its full length for receiving fluid which is passed through the filler material. It also has a system of longitudinal baffles designed to increase the length of flow of the fluid through the filter. The baffles have an access common to that of the core and extend the length thereof.
These prior art patents suffer from two similar problems. First, the corrosive nature of the silver-containing solution will quickly create a passageway through the filler material to the outlet. The solution will always flow in the path of least resistance. As more and more of the filler material corrodes, the flow path will follow a hole extending through the filler material which offers little resistance nor receives much of the silver deposit.
Secondly, if the silver-containing solution reaches the filler material before the silver is plated out, the silver will plate to the highly corrosive filler material. As the filler material is depleted, the silver and the filler material will fall to the bottom of the container. As such, it becomes almost impossible for the user to determine the amount of silver that has been recovered.
It is an object of the present invention to provide a silver recovery system that effectively removes a large amount of silver from a silver-containing solution.
It is another object of the present invention to provide a silver recovery system in which the silver-containing solution must traverse a lengthy path of deposition prior to exit from the system.
It is a further object of the present invention to provide a silver recovery system that is relatively inexpensive.
It is still another object of the present invention to provide a silver recovery system that enables much of the silver content of the silver-containing solution to plate onto a removable shield.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.